The invention relates generally to amplifiers, and particularly relates to a rail-to-rail output stage of an amplifier.
Amplifiers are ubiquitous in the electronics industry for both amplifying and buffering an input signal, as well as providing an output signal within a range of voltage or current (swing).
Of particular interest is to operate an amplifier with a maximum output swing between a given set of supplies. This function is referred to as rail-to-rail performance in accordance with the operation of the device between the positive and negative voltage supplies (or rails).
A conventional rail-to-rail gain stage of an amplifier is disclosed in U.S. Pat. No. 5,440,273, which discloses an operational amplifier with a rail-to-rail output stage. The '273 patent discloses an output (or gain) stage that includes a translinear bias voltage source, a voltage buffer and a pair of output transistors. Conventional output stages of amplifiers, however, continue to suffer from certain design constraints relating to output response performance, required power, output current sourcing and the number and size of components of the circuit, as well as frequency response and stability.
It is, therefore, an objective of the present invention to provide an output stage that is capable of low voltage operation.
It is also objective of the invention to provide an amplifier output stage that processes signals operating substantially near the power supply rails.
It is another objective of the invention to provide an output stage with a compact design having relatively few transistors.
It is further an objective of the invention to provide an output stage that has the ability to sink and source large currents while operating on a small bias voltage.
It is a further objective of the invention to reduce or eliminate the sensitivity of the quiescent current in an output stage to loading conditions on the output.
It is a further objective of the invention to reduce or eliminate the sensitivity of an output stage to variations in processing such as variations in resistor values or transistor matching during manufacturing.